Drosophila PRL-1 is a growth inhibitor that counteracts the function of the Src oncogene

Deletion of PTP4A3 phosphatase in high-grade serous ovarian cancer cells decreases tumorigenicity and produces marked changes in intracellular signaling pathways and cytokine release

The oncogenic protein tyrosine phosphatase PTP4A3 is frequently overexpressed in human ovarian cancers and is associated with poor patient prognosis. PTP4A3 is thought to regulate multiple oncogenic signaling pathways, including STAT3, SRC, and extracellular signal-regulated kinase. The objective of this study was to generate ovarian cancer cells with genetically depleted PTP4A3, to assess their tumorigenicity, to examine their cellular phenotype, and to uncover changes in their intracellular signaling pathways and cytokine release profiles. Genetic deletion of PTP4A3 using CRISPR/CRISPR-associated protein 9 enabled the generation of individual clones derived from single cells isolated from the polyclonal knockout population. We observed a >90% depletion of PTP4A3 protein levels by western blotting in the clonal cell lines compared with the sham-transfected wild-type population. The wild-type and polyclonal knockout cell lines shared similar monolayer growth rates, whereas the isolated clonal populations 2B4, 3C9, and 3C12 exhibited significantly lower monolayer growth characteristics consistent with their lower PTP4A3 levels. The clonal Ptp4a3 knockout cell lines also had substantially lower in vitro colony formation efficiencies compared with the wild-type cells and were less tumorigenic in vivo. The clonal knockout cells were markedly less responsive to interleukin-6-stimulated migration in a scratch wound assay compared with the wild-type cells. Antibody microarray assays documented differences in cytokine release and intracellular phosphorylation patterns in the Ptp4a3-deleted clones. Bioinformatic network analyses indicated alterations in cellular signaling nodes. These biochemical changes could ultimately form the foundation for pharmacodynamic endpoints useful for emerging anti-PTP4A3 therapeutics. SIGNIFICANCE STATEMENT: Clones of high-grade serous ovarian cancer cells were isolated, in which the oncogenic phosphatase Ptp4a3 gene was deleted using CRISPR/CRISPR-associated protein 9 methodologies. The Ptp4a3-null cells exhibited loss of in vitro proliferation, colony formation, and migration and reduced in vivo tumorigenesis. Marked differences in intracellular protein phosphorylation and cytokine release were seen. The newly developed Ptp4a3 knockout cells should provide useful tools to probe the role of PTP4A3 phosphatase in ovarian cancer cell survival, tumorigenicity, and cell signaling.

Drosophila Phosphatase of Regenerating Liver Is Critical for Photoreceptor Cell Polarity and Survival during Retinal Development

Establishing apicobasal polarity, involving intricate interactions among polarity regulators, is key for epithelial cell function. Though phosphatase of regenerating liver (PRL) proteins are implicated in diverse biological processes, including cancer, their developmental role remains unclear. In this study, we explore the role of Drosophila PRL (dPRL) in photoreceptor cell development. We reveal that dPRL, requiring a C-terminal prenylation motif, is highly enriched in the apical membrane of developing photoreceptor cells. Moreover, dPRL knockdown during retinal development results in adult Drosophila retinal degeneration, caused by hid-induced apoptosis. dPRL depletion also mislocalizes cell adhesion and polarity proteins like Armadillo, Crumbs, and DaPKC and relocates the basolateral protein, alpha subunit of Na⁺/K⁺-ATPase, to the presumed apical membrane. Importantly, this polarity disruption is not secondary to apoptosis, as suppressing hid expression does not rescue the polarity defect in dPRL-depleted photoreceptor cells. These findings underscore dPRL's crucial role in photoreceptor cell polarity and emphasize PRL's importance in establishing epithelial polarity and maintaining cell survival during retinal development, offering new insights into PRL's role in normal epithelium.

A novel role of PRL in regulating epithelial cell density by inducing apoptosis at confluence

Maintaining proper epithelial cell density is essential for the survival of multicellular organisms. While regulation of cell density through apoptosis is well known, its mechanistic details remain elusive. Here, we report the involvement of membrane-anchored phosphatase of regenerating liver (PRL), originally known for its role in cancer malignancy, in this process. In epithelial MDCK cells, upon confluence, doxycycline-induced expression of PRL upregulated apoptosis, reducing the cell density. This could be circumvented by artificially reducing the cell density via stretching the cell-seeded silicon chamber. Moreover, siRNA-mediated knockdown of endogenous PRL blocked apoptosis, leading to greater cell density. Mechanistically, PRL promoted apoptosis by upregulating the translation of E-cadherin and activating TGF-β pathway. Morpholino-mediated inhibition of PRL expression in zebrafish embryos caused developmental defect with reduced apoptosis and increased epithelial cell density during convergent extension. This study revealed a novel role of PRL in regulating density-dependent apoptosis in vertebrate epithelium.

Phosphatase of Regenerating Liver-1 Selectively Times Circadian Behavior in Darkness via Function in PDF Neurons and Dephosphorylation of TIMELESS

The timing of behavior under natural light-dark conditions is a function of circadian clocks and photic input pathways, but a mechanistic understanding of how these pathways collaborate in animals is lacking. Here we demonstrate in Drosophila that the Phosphatase of Regenerating Liver-1 (PRL-1) sets period length and behavioral phase gated by photic signals. PRL-1 knockdown in PDF clock neurons dramatically lengthens circadian period. PRL-1 mutants exhibit allele-specific interactions with the light- and clock-regulated gene timeless (tim). Moreover, we show that PRL-1 promotes TIM accumulation and dephosphorylation. Interestingly, the PRL-1 mutant period lengthening is suppressed in constant light, and PRL-1 mutants display a delayed phase under short, but not long, photoperiod conditions. Thus, our studies reveal that PRL-1-dependent dephosphorylation of TIM is a core mechanism of the clock that sets period length and phase in darkness, enabling the behavioral adjustment to change day-night cycles.

A Novel Neuroprotective Role of Phosphatase of Regenerating Liver-1 against CO2 Stimulation in Drosophila

Neuroprotection is essential for the maintenance of normal physiological functions in the nervous system. This is especially true under stress conditions. Here, we demonstrate a novel protective function of PRL-1 against CO₂ stimulation in Drosophila. In the absence of PRL-1, flies exhibit a permanent held-up wing phenotype upon CO₂ exposure. Knockdown of the CO₂ olfactory receptor, Gr21a, suppresses the phenotype. Our genetic data indicate that the wing phenotype is due to a neural dysfunction. PRL-1 physically interacts with Uex and controls Uex expression levels. Knockdown of Uex alone leads to a similar wing held-up phenotype to that of PRL-1 mutants. Uex acts downstream of PRL-1. Elevated Uex levels in PRL-1 mutants prevent the CO₂-induced phenotype. PRL-1 and Uex are required for a wide range of neurons to maintain neuroprotective functions. Expression of human homologs of PRL-1 could rescue the phenotype in Drosophila, suggesting a similar function in humans.

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PRL-1 functions to protect the nervous system against olfactory CO₂ stimulation

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PRL-1 physically interacts with Uex and controls Uex expression levels

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PRLs may retain a similar neuroprotective function in humans

Branch-restricted localization of phosphatase Prl-1 specifies axonal synaptogenesis domains

Central nervous system (CNS) circuit development requires subcellular control of synapse formation and patterning of synapse abundance. We identified the Drosophila membrane-anchored phosphatase of regenerating liver (Prl-1) as an axon-intrinsic factor that promotes synapse formation in a spatially restricted fashion. The loss of Prl-1 in mechanosensory neurons reduced the number of CNS presynapses localized on a single axon collateral and organized as a terminal arbor. Flies lacking all Prl-1 protein had locomotor defects. The overexpression of Prl-1 induced ectopic synapses. In mechanosensory neurons, Prl-1 modulates the insulin receptor (InR) signaling pathway within a single contralateral axon compartment, thereby affecting the number of synapses. The axon branch–specific localization and function of Prl-1 depend on untranslated regions of the prl-1 messenger RNA (mRNA). Therefore, compartmentalized restriction of Prl-1 serves as a specificity factor for the subcellular control of axonal synaptogenesis.

Suppression of protein tyrosine phosphatase N23 predisposes to breast tumorigenesis via activation of FYN kinase

Zhang et al. identified PTPN23 as a suppressor of cell motility and invasion in mammary epithelial and breast cancer cells. They validated the underlying mechanism of PTPN23 function in breast tumorigenesis as that of a key phosphatase that normally suppresses the activity of FYN in two different models.

Disruption of the balanced modulation of reversible tyrosine phosphorylation has been implicated in the etiology of various human cancers, including breast cancer. Protein Tyrosine Phosphatase N23 (PTPN23) resides in chromosomal region 3p21.3, which is hemizygously or homozygously lost in some breast cancer patients. In a loss-of-function PTPome screen, our laboratory identified PTPN23 as a suppressor of cell motility and invasion in mammary epithelial and breast cancer cells. Now, our TCGA (The Cancer Genome Atlas) database analyses illustrate a correlation between low PTPN23 expression and poor survival in breast cancers of various subtypes. Therefore, we investigated the tumor-suppressive function of PTPN23 in an orthotopic transplantation mouse model. Suppression of PTPN23 in Comma 1Dβ cells induced breast tumors within 56 wk. In PTPN23-depleted tumors, we detected hyperphosphorylation of the autophosphorylation site tyrosine in the SRC family kinase (SFK) FYN as well as Tyr142 in β-catenin. We validated the underlying mechanism of PTPN23 function in breast tumorigenesis as that of a key phosphatase that normally suppresses the activity of FYN in two different models. We demonstrated that tumor outgrowth from PTPN23-deficient BT474 cells was suppressed in a xenograft model in vivo upon treatment with AZD0530, an SFK inhibitor. Furthermore, double knockout of FYN and PTPN23 via CRISPR/CAS9 also attenuated tumor outgrowth from PTPN23 knockout Cal51 cells. Overall, this mechanistic analysis of the tumor-suppressive function of PTPN23 in breast cancer supports the identification of FYN as a therapeutic target for breast tumors with heterozygous or homozygous loss of PTPN23.

Phosphatases: Their Roles in Cancer and Their Chemical Modulators

Phosphatases are involved in basically all cellular processes by dephosphorylating cellular components such as proteins, phospholipids and second messengers. They counteract kinases of which many are established oncogenes, and therefore kinases are one of the most important drug targets for targeted cancer therapy. Due to this relationship between kinases and phosphatases, phosphatases are traditionally assumed to be tumour suppressors. However, research findings over the last years prove that this simplification is incorrect, as bona-fide and putative phosphatase oncogenes have been identified. We describe here the role of phosphatases in cancer, tumour suppressors and oncogenes, and their chemical modulators, and discuss new approaches and opportunities for phosphatases as drug targets.

The Hippo pathway promotes cell survival in response to chemical stress

Cellular stress defense mechanisms have evolved to maintain homeostasis in response to a broad variety of environmental challenges. Stress signaling pathways activate multiple cellular programs that range from the activation of survival pathways to the initiation of cell death when cells are damaged beyond repair. To identify novel players acting in stress response pathways, we conducted a cell culture RNA interference (RNAi) screen using caffeine as a xenobiotic stress-inducing agent, as this compound is a well-established inducer of detoxification response pathways. Specifically, we examined how caffeine affects cell survival when Drosophila kinases and phosphatases were depleted via RNAi. Using this approach, we identified and validated 10 kinases and 4 phosphatases that are essential for cell survival under caffeine-induced stress both in cell culture and living flies. Remarkably, our screen yielded an enrichment of Hippo pathway components, indicating that this pathway regulates cellular stress responses. Indeed, we show that the Hippo pathway acts as a potent repressor of stress-induced cell death. Further, we demonstrate that Hippo activation is necessary to inhibit a pro-apoptotic program triggered by the interaction of the transcriptional co-activator Yki with the transcription factor p53 in response to a range of stress stimuli. Our in vitro and in vivo loss-of-function data therefore implicate Hippo signaling in the transduction of cellular survival signals in response to chemical stress.

Dual-specificity phosphatases as molecular targets for inhibition in human disease

SIGNIFICANCE

The dual-specificity phosphatases (DUSPs) constitute a heterogeneous group of cysteine-based protein tyrosine phosphatases, whose members exert a pivotal role in cell physiology by dephosphorylation of phosphoserine, phosphothreonine, and phosphotyrosine residues from proteins, as well as other non-proteinaceous substrates.

RECENT ADVANCES

A picture is emerging in which a selected group of DUSP enzymes display overexpression or hyperactivity that is associated with human disease, especially human cancer, making feasible targeted therapy approaches based on their inhibition. A panoply of molecular and functional studies on DUSPs have been performed in the previous years, and drug-discovery efforts are ongoing to develop specific and efficient DUSP enzyme inhibitors. This review summarizes the current status on inhibitory compounds targeting DUSPs that belong to the MAP kinase phosphatases-, small-sized atypical-, and phosphatases of regenerating liver subfamilies, whose inhibition could be beneficial for the prevention or mitigation of human disease.

CRITICAL ISSUES

Achieving specificity, potency, and bioavailability are the major challenges in the discovery of DUSP inhibitors for the clinics. Clinical validation of compounds or alternative inhibitory strategies of DUSP inhibition has yet to come.

FUTURE DIRECTIONS

Further work is required to understand the dual role of many DUSPs in human cancer, their function-structure properties, and to identify their physiologic substrates. This will help in the implementation of therapies based on DUSPs inhibition.

Early changes in the pupal transcriptome of the flesh fly Sarcophagha crassipalpis to parasitization by the ectoparasitic wasp, Nasonia vitripennis

We investigated changes in the pupal transcriptome of the flesh fly Sarcophaga crassipalpis, 3 and 25 h after parasitization by the ectoparasitoid wasp, Nasonia vitripennis. These time points are prior to hatching of the wasp eggs, thus the results document host responses to venom injection, rather than feeding by the wasp larvae. Only a single gene appeared to be differentially expressed 3 h after parasitization. However, by 25 h, 128 genes were differentially expressed and expression patterns of a subsample of these genes were verified using RT-qPCR. Among the responsive genes were clusters of genes that altered the fly's metabolism, development, induced immune responses, elicited detoxification responses, and promoted programmed cell death. Envenomation thus clearly alters the metabolic landscape and developmental fate of the fly host prior to subsequent penetration of the pupal cuticle by the wasp larva. Overall, this study provides new insights into the specific action of ectoparasitoid venoms.